Electric heater



(No Modem W. RI 2 Sheets-Sheet 1.

ELEGTRIG HEATER.. 110.579,611. Patented Mam.30,1897.

Il C n\ n\ -111-111.11- 6 (No Model.) 2 Sheets-Sheet 2.

W. R. SMITH.

ELECTRIC HEATER.

No. 579,611. Patented Mar. 30, T897.

W j NVENTUR:

Vbodying the invention.

UNITED STATES PATENT OEEIcE.

IVILLIAM R. SMITH, F MANCHESTER, NEIV HAMPSHIRE.

ELECTRIC HEATER.

SPECIFICATION forming part of Letters Patent No. 579,61 1, dated March SO, 1897.

Application filed June 11,1896. Serial No. 595,178. (No model.)

To all whom, t may concern:

Be it known that I, WILLIAM R. SMITH, of Manchester, in the county of Hillsborough and State of New Hampshire, have invented certain new and useful Improvements in Electrical Heaters, of which the following is a specification.

This invention relates to electrical heating apparatus comprising a boiler or chamber containing water-heating tubes, each of which consists of an inner tube and an outer tube provided with an electrical resistance contained in a space between said tubes, the said resistance being arranged to form an outer helix on the inner surface of the outer tube and an inner helix on the outer surface of the inner tube.

The present invention has for its objects, first, to enable the two helices to be made of a single integral piece without joints or couplings of any kind and without the formation of an angle in that part of the resistance that connects the outer ends of the helices, and, secondly, to provide mea-nsforinsulating said helices and holding them securely in their proper relative positions.

To these ends the invention consist-s in the improvements which I will now proceed to describe and claim.

Of the accompanying drawings, forming a part of this specification, Figure 1 represents a vertical section of a heating apparatus emfig. 2 represents an enlarged vertical section of one ot the heating-tu bes. Fig. 3 represents a section on line 3 3 of Fig. 2. Fig. a represents a side view of a portion of the resistance. Fig. 5 represents an end view of the same.

Similar reference letters and figures indicate the same parts throughout the several views.

In the drawings the boiler-casing l, which may be a casting provided with suitable feet, is formed with a dome-shaped upper end 2 and a horizontal iioor or lower wall 8, said wall being provided with a pluralityT of screw-threaded openings to receive the tubular electric heaters hereinafter described. t indicates the eXitpipe from the upper end of the cas ing, and 5 the inletpipe, said pipes being adapted to be connected with any suitable radiator. This shape of the casing prevents the formation of any still bodies of water in any portion of the casing, since the domeshaped top causes the water as it is heated to rise and flow through the pipe 4@ at an accelerated rate of speed.

Each of the heaters is composed of a base or holder a, formed as a plug adapted to be screwed into an opening in the lower wall of the casing and provided with a squared end h', by means of which the heater may be turned into or out of place by means of an ordinary wrench. to receive an outer tube c and an inner concentric tube c', the space c2 between said tubes being provided with the resistance-wire hereinafter described. The upper endfi of the two tubes are covered by means of a cap d, having flanges d d2 to fit over the ends of the tubes to prevent the access of water to the sgace between them. Through the wall of the plug a passage or conduit e is formed, said conduit being below the space e2 and forming a passage for the circulation of water from the outside to the interior of the tube c.

The interior ofthe outer tube c is provided with a lining of suitable insulating material having a helical groove formed as acoarse right-hand screw-thread for the reception of the outer helix of the resistance f, and the outer surface of the inner tube c is provided with a coating of suitable insulating material having a helical groove formed as a coarse left-hand thread to form a groove Vfor the inner helix of the said resistance.

f represents the resistance-wire, which is a single piece of platinum or other suitable material, extending continuously, without joint or weld, from one end where it coni- Inences and is coiled in contact with the lower end of the inner wall of the outer tube to where it terminates in contact with the lower end of the outer wall of the inner tube, said piece comprising an outer helix and an inner helix. The convolutions oi' the outer helix are contained in thchelical grooves in the inner surface of the outer tube, while those of the inner helix are contained in the helical groove in the outer surface of the inner tube.

The arrangement of the resistance in two helices, one of a pitch which is opposite that of the other, enables the entire resistance to be made of a single piece of wire without a This plug is screw-threaded IOD joint or coupling at the outer ends of the helices, the change of direction of the pitch enabling the portion of the wire that connects the two helices to cross the intervening space at a gradual curve and without angular deviation from the curvature ot the convolutions which it connects.

lt will be seen that if both helices had the same pitch it would be necessary to either abruptly bend the portion oi the wire which connects the outer convolutions of the helices or to make the helices in separate pieces and unite their ends by a solder-joint or by a coupling. ln either case Ithe connection between the two helices necessarily projects outwardly from the ends olA the helices and makes the resistance undesirably long a'- l bulky. l have found that an abrupt bend in a resistance olf this character is 'further objectionable because of the liability et the resistance to burn away at the bend, this being due, as l believe, to the abrupt change in the direction of the current. ji joint or union of two pieces is also objectionable, because, if a solder-joint, it is liable to vary in diameter and burn away at the smallest part, and it is also liable to be destroyed by the 'fusing of the solder. lt two pieces are united by a coupling havin screws or rivets, the latter become loose by the act-ion of the current, and the joint becomes unreliable and often useless. l avoid these ditiiculties by making the two helices ol opposite pitch, whereby l am enabled to make the entire resistance, including the portion that connects the outer convolutions, in a single seamless or jcintless piece, free from abrupt bends, the connection between the outer ends oi the helices adding nothing to the length or bulk of the structure.

rlhe insulating-comings having the helical `grooves conforming to the pitch of the helices ofthe resistance provide i'or securely holding the convolutions of the resistance and preventing contact between them.

l have found that in case et a dat ribbonlike wire there lis a liability of the edges becoming unduly heated and fused. l have found thatv by making the resistance-wire in ribbon form, but with its edges thicker than its center, this difficulty is avoided and the durability of the resistance is greatly prolonged.

The ends ofthe resistance-wire pass through suitable cylindrical blocks or insulators fi in the plug andare connected to circuit-wires fi".

The portion of the wire which passes through the insulators l term the conduetor, as at f, and this may or may not be integral with the ribbon-like portion or" the resistance. As shown in Fig. 2, the conductor f is considerably larger in diameter than the portion of the resistance within the space c2, the object of this being to more readily conduct the current where it passes through the plug and to thereby prevent heating at points where heat is not desired.

The casing is preferably made in a single casting, which includes the body l, dome 2, and bottom 5, and may be made ol any suitable metal. l thus insure a water-tight construction, so i'ar as the casing is concerned, there beingnojoints, rivet-holes, the., the only joints being those between the heater-plugs and the bottom of the easing. These joints are made water-tight by cutting the threaded openings in. the bottom of the casing and the threaded portions oi' the plugs on a slight taper, so that when the plugs are screwed home they will have a water-tight connection with the bottoni oig the casing.

l claiml. in an electrical heating' apparatus, an electrical resistance composed el a single joint-less piece disposed in two helices of opposite pitch, one within the other.

2. fin electrical heating apl'iaratns comprising in its construction a plug provided with inner and outer tubes forming an annular chamber, and a resistance composed ot' a singie jointless piece disposed in two helices ol' opposite pitch, one helix being at the outer side and the other at the inner side ol' said chamber.

El. rin electricalheating apparatus comprising in its construction a plug provided with inner and outer tubes i' 1n'niii1g an annular chamber the walls of which are provided with insulating' material, one wall being provided with a helical groove and the other with a helical groove ol opposite pitch, and a resistance in said grooves composed ot' a single piece formed into two helices oi opposite pitch.

ln testimony whereof l have signed my naine to this speciiication, in the presence ot' two subscribing witnesses, this lf'lth day of May, D 18%.

Vfitnesses:

A. D. lliirufuson, P. W. Pnzzniri.

IOO 

